An in-vehicle power conversion system to be equipped in an electric vehicle is equipped with various sorts of power conversion apparatuses, such as an inverter which is for driving a motor, a DC/DC converter which steps down from a high battery voltage to a 12 V system battery voltage, a DC/DC converter which steps up from the 12 V system battery voltage to the high battery voltage, a charger which is for charging from a commercial power source to a high voltage battery, and an inverter which generates from the high voltage battery to an AC 100 V. In the internal configuration of these power conversion apparatuses, there is generally used a switching circuit, such as a chopper circuit or a bridge circuit, whose generated high frequency noise is large; and various filter circuits and shield structures are used for their countermeasures against the noise.
In circumstances surrounding current electric vehicles, requirements for reduction in size and cost of components thereof are extremely strong and various types of power conversion apparatuses to be equipped in electric vehicles are also no exception. One of important techniques of means of achieving reduction in size and cost of these power conversion apparatuses is a speeding up of switching frequency. The speeding up of the switching frequency can reduce in size and cost of large and expensive transformer and reactor; and thus, the speeding up is one of extremely important technical development elements for various types of power conversion apparatuses.
However, conductive noise and radiation noise including a surge voltage increase and become high frequency in a power system circuit of the power conversion apparatus which performs switching of a large current and a high voltage; and accordingly, the conductive noise and the radiation noise including the surge voltage are superimposed on a peripheral circuit of the power system circuit and a control circuit due to indirect causes such as via stray capacitance, via GND and a housing, or crosstalk and a failure that damages the stable operation of the circuit is generated. Furthermore, when the conductive noise or the radiation noise due to the large current switching is superimposed on a filter circuit of input and output, there exists a problem in that filter characteristics are deteriorated and original filter performance cannot be exerted due to a phenomenon in which noise is superimposed again on a line in which filtering is performed.
As countermeasures against such noise interference, countermeasures such as suppression of noise interference by the use of a local shield at the inside of the apparatus, filter enhancement, and the ingenuity of circuit layouts are conducted. For example, FIG. 14 is one example that achieves the local shield at the inside of the apparatus and shows a configuration sectional view of a conventional in-vehicle power conversion system.
In FIG. 14, reference numeral 211 denotes a housing and 212 denotes a housing cover, both of which use a conductive component and have a role to shield the whole apparatus. In this case, 203 denotes a filter circuit unit; 204 denotes a power system main circuit unit; 205 denotes a control circuit unit; 213 denotes a shield case for the filter circuit; and 214 denotes a shield case for the power system main circuit. In the thus configured apparatus, noise generated in the power system main circuit unit 204 is shielded by the shield case for the power system main circuit 214; and the noise does not give an influence on the control circuit unit 205 and the filter circuit unit 203.
Noise generated in the control circuit unit 205 is shielded from leaking to the outside by the housing 211 and the housing cover 212, both of which shield the whole apparatus, and the noise does not give an influence on other circuit units by the shield case for the power system main circuit 214 and the shield case for the filter circuit 213. The filter circuit unit 203 itself does not generate noise. However, when the filter circuit unit 203 receives the influence of noise from other circuit units, filter performance according to the attenuation characteristics of the filter cannot be exerted; and thus, noise propagation from other circuits is shielded by the shield case for the filter circuit 213.
Incidentally, undermentioned Patent Document 1 is one in which a shield space is formed by a chassis and a shield case. Patent Document 2 is one in which a cut-out portion is formed in a shield metal to suppress high frequency noise of a choke coil in a low pass filter circuit.